Acoustic guitars have been provided with pickups and preamplifiers for many years. The preamplifiers typically have a control unit which for example, may include means for controlling volume, bass, middle range and treble. The controllers are typically slide or rotary potentiometers and various kind of switches. In some preamplifiers, displays, such as LCD displays, may be used to show various parameters.
Installing current preamplifiers require typically a relatively large hole that has to be routed into the side of the guitar, into which the control unit is installed. Because acoustic guitars are often very valuable and sensitive for changes, large holes make them less valuable and their sound characteristics may become worse.
During the past years, there have been different configurations offering suitable controls to adjust the preamplifier parameters having as few holes as possible, or alternately having no holes at all. Companies like L.R. Baggs and Shadow have, for example, manufactured different control units that can be installed into the guitar sound hole itself. However, the problem in such cases is that the controllers become very small, the slide controls are difficult to use, and/or contain limited options for controlling numerous parameters, due to the limited size. In electric guitars there have been ideas to integrate controllers to the pick guard. As an example, US Patent Publication No. 2004/0003703 describes a pick guard with built in controllers.
U.S. Pat. No. 5,917,437 discloses a keyboard structure that is resistant to hard impacts where, under a solid and hard surface, there is a transducer element with a pattern, corresponding a keyboard, that is silk-screen printed with silver paste. In an exemplary structure disclosed herein, a so-called electret bubble film is used, which is described generally in U.S. Pat. No. 4,654,546. Under this structure, a constant electric charge can be injected into a dielectric electret bubble film, such as polypropene, and may include flat and/or torn gas blisters.
It is noted that the configuration disclosed in U.S. Pat. No. 5,917,437 has many disadvantages when applied to a versatile device, especially one having thin construction and is mass-produced. The prior art does not allow having as thin and economical transducer structure as possible, nor does the prior art provide a configuration for having economical, small current consumption in the electronics. Additionally, the prior art does not disclose the use of glide controllers for assisting users in adjusting electro-acoustic parameters.
A method is disclosed in WO publication 9606718 for swelling a foamed plastic film wherein the amount of gas it contains can be increased. EP Patent publication EP-B1-0775049 discloses how a thin film, including flat gas bubbles and oriented biaxially is charged electrically so that partial discharges may occur inside it.
Other prior art discloses keyboards arrangements that rely on capacitance to effect voltage flow through a connection when the surface is touched by a user. Additionally, piezoelectric keypads may be formed with laminated layers or printable paste or paint that includes piezoelectric crystals, to enable a turn-on voltage or charge. Examples of such keyboards are ALGRA Dynasim™ and ALGRA Dynapic™ keyboards currently being produced by ALGRA Ltd in Switzerland.